Catheters or other medical devices for placement into a patient's vascular system are used for many procedures. Frequently these devices are left in place for extended periods, especially when the procedures are performed on a periodic basis and can include several treatments per week. For example, some catheters are used in the simultaneous introduction of fluid into the body and withdrawal of fluid from the body. Such indwelling catheters are particularly useful in hemodialysis. The hemodialysis catheter is typically inserted partially within the body with the distal end placed in a blood vessel and the proximal end external to the body and connectable to another device such as a dialysis unit. An indwelling hemodialysis catheter is advantageous in that the patient does not need to have repeated needle insertions into the skin to gain access to the vasculature each time a dialysis procedure is initiated. Any type of indwelling medical device has the advantage of allowing repeated treatments using the same device for access to the body without the need for reinserting the device for each treatment.
However, several disadvantages are associated with leaving an indwelling device in place for an extended period of time. Patients may develop an infection at the insertion site or in the tissue surrounding the indwelling device. In addition, clots or a fibrous sheath may develop and occlude openings in the catheter and provide additional sources for infections to develop. The fibrous sheath originates from the insertion point at the patient's skin and migrates distally along the device until the openings in the device become occluded. The fibrous sheath typically begins to develop within twenty-four hours of insertion of the device into the patient with an initial thrombus present which is composed of platelets, fibrin, red blood cells, and white blood cells. After three days, the thrombi continue to thicken forming a fibrous sheath and within one week, smooth muscle cells infiltrate the fibrous sheath. The surface of the fibrous sheath is covered with endothelial cells oriented in the direction of blood flow. Within two weeks, the sheath is a mixture of smooth muscle cells and collagen and at three to four weeks, the volume of collagen increases and becomes organized in thicker, coiled bundles. After two to six months collagen is the main component. Sufficient migration and development of the fibrous sheath become evident with a decrease in flow rate through the device to indicate that an opening has become at least partially occluded.
Occluding the opening(s) presents the additional problem that successive treatments require substantially more time to adequately perform the procedure and may increase the costs relating to the treatment. The openings may become completely occluded, for example, by the sheath, so that the device must be removed and a new device inserted. Treatments including pharmaceutical compositions have been used during each procedure to try to disrupt the sheath or clot. However, some pharmaceutical compositions may further complicate the treatment and add to the costs of the procedure.
What is needed is an improved medical device and associated methods that disrupt the migration and inhibit the formation of the occluding materials, such as a fibrous sheath, around the device and allow flow to continue through the device at a sufficiently high rate for treatment.